This invention relates to an optical disk drive.
Generally, an optical disk drive writes and reads data on an optical disk by means of a laser beam. The optical disk drive includes a light source module that emits the laser beam and an optical head carrying an object lens that converges the laser beam on a small light spot on the optical disk.
The tracking operation of the optical disk drive includes (1) a rough tracking operation and (2) a fine tracking operation. The rough tracking operation is accomplished by moving the optical head crossing the tracks of the optical disk. The fine tracking operation is accomplished by minutely moving the light spot on the optical disk. For this purpose, a galvano mirror is provided in a light path between the light source module and the object lens. By rotating the galvano mirror, the angle of incidence of the laser beam incident on the object lens is changed, so that the light spot on the optical disk is moved.
FIG. 1 is a perspective view of a conventional galvano mirror unit disclosed in Japanese Patent Laid-Open Publication No. 64-2105. The galvano mirror 41 is supported by a pair of elongated plate springs 42. The plate springs 42 are extended from opposing side ends of the galvano mirror 41 in such a manner that center lines of the plate springs 42 are aligned with each other. Distal ends of the plate springs 42 are fixed to a base 43. The plate springs 42 is deformable, so that the plate springs 42 can be twisted about an axis 42A defined by the center lines of the plate springs 42. Due to the twist (elastic deformation) of the plate springs 42, the rotation of the galvano mirror 41 about an axis 42A is enabled.
In order to actuate the galvano mirror 41, coils 45 and 46 are fixed to the galvano mirror 41. Further, a yoke 44 is provided on the base 43, which has a pair of magnets (not shown) generating a magnetic field in which the coils 45 and 46 are positioned. The galvano mirror 41 is rotated by the electromagnetic induction caused by the current flow in the coils 45 and 46 and the magnetic field caused by the magnets of the yoke 44.
However, since the rotation of the galvano mirror 41 is caused by the elastic deformation of the plate springs 42, there exists a primary resonance frequency that causes an unstable rotation of the galvano mirror 41.
In order to lower the primary resonance frequency, it is necessary to increase deformability of the plate springs 42. For that purpose, it is necessary to increase the axial length of the plate springs 42, which may increase the total size of the galvano mirror unit. Thus, a compact galvano mirror unit that enables a stable tracking operation is desired.
It is therefore an object of the present invention to provide a compact galvano mirror unit that enables a stable tracking operation.
According to one aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, and a pair of receive members provided to the other of the rotor and the stator. The receiving members respectively receive the center pins. The rotor is pivoted by the engagement of the center pin and the receive member.
Since the rotor is pivoted by the center pins and the receive members, there is no primary resonance frequency (which generates in a conventional galvano mirror) that causes an unstable rotation of the galvano mirror. Thus, it is possible to obtain a stable tracking operation.
In the conventional spring-supported galvano mirror, it is necessary to lengthen the spring member in order to lower the primary resonance frequency. However, according to the above-described arrangement, it is not necessary to increase the size of the galvano mirror unit (since there is no primary resonance frequency). Accordingly, the size of the galvano mirror unit can be compact.
In a particular arrangement, the galvano mirror unit further includes a pair of driving coils provided to one of the rotor and the stator, and a pair of driving magnets provided to the other of the rotor and the stator. By allowing current to flow in the driving coils, the rotor can be rotated about the rotation axis.
It is preferable that the center pins have curved projections. In such case, the receive members have conical surfaces. Further, the conical surfaces of the receive members respectively contact the curved projections of the center pins.
According to another aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (which respectively receive the first and second center pins) provided to the rotor, and a biasing member provided to the stator. The biasing member is arranged to bias the first center pin to the first receive member.
As constructed above, due to the biasing member, it is possible to eliminate the backlash between the first center pin and the first receive member and between the second center pin and the second receive member.
In a particular arrangement, the biasing member includes a plate spring. Further, the first center pin and the plate spring are mechanically coupled with each other. With such an arrangement, the inclination of the upper center pin is prevented. Therefore, the rotation of the galvano mirror is stabilized.
According to further aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and an offset member provided to the stator. The first center pin is provided in a hole of the stator so that the first center pin is movable in the direction of the rotation axis. The offset member urges the first center pin so that the center pin is inclined in a predetermined direction in the hole.
With such an arrangement, since the first center pin is inclined in a predetermined direction, the deviation of the inclination of the first center pin is prevented. Therefore, the rotation of the galvano mirror is stabilized.
According to other aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and a plate spring provided to the stator. The plate spring biases the first center pin to the first receive member. The first center pin is fixed to the plate spring.
With such an arrangement, since the first center pin is fixed to the plate spring, the inclination of the rotation axis of the rotor is prevented. Therefore, the rotation of the galvano mirror is stabilized.
According to still further aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, a pair of receive members (respectively receiving the center pins) provided to the other of the rotor and the stator, a pair of driving magnets provided at opposing ends of the rotor, and a pair of driving coils provided to the stator. The driving coils are faced with the driving magnets respectively.
With such an arrangement, since the driving coils are not provided to the rotor but provided to the stator, the arrangement for electrical connection (for supplying electricity to the driving coils) becomes simple.
According to still yet further aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, a pair of receive members (respectively receiving the center pins) provided to the other of the rotor and the stator, and first and second driving coils provided to the stator. The rotor has first and second sides that are respectively faced with the first and second coils. The first and second sides being magnetized.
With such an arrangement, since it is not necessary to provide separate driving magnets to the rotor, the structure of the mirror holder can be simplified.
According to yet further aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror block having a mirror surface, a stator that rotatably supports the galvano mirror block about a rotation axis, first and second center pins provided to the stator, and first and second receive portions provided to the galvano mirror block. The first and second receive portions respectively receive the first and second center pins.
With such an arrangement, since it is not necessary to provide a mirror holder or the like for holding the galvano mirror, the structure of the galvano mirror unit can be simplified.
According to still other aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, a biasing magnet provided to the stator so that the biasing magnet is located around the first center pin, and a magnetic chip provided to a predetermined portion of the first center pin. Due to the magnetic force generated by the biasing magnet and the magnetic chip, the first center pin is biased to the first receive member.
With such an arrangement, since the biasing force can be obtained by the biasing magnet and the magnet chip, it is not necessary to provide a separate spring member for biasing the first center pin. Thus, the structure of the galvano mirror unit can be simplified.
According to still another aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, a biasing coil provided to the stator, and a magnetic chip provided to a predetermined portion of the first center pin. By allowing current to flow in the biasing coil, the first center pin is biased to the first receive member.
With such an arrangement, since the biasing force can be obtained by the biasing coil and the first center pin, it is not necessary to provide a separate spring member for biasing the upper center pin. Thus, the structure of the galvano mirror unit can be simplified. Further, since the biasing force can be adjusted by varying the current flow in the biasing coil, the friction produced when the mirror holder is rotated can be adjusted.
According to still another aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator. The first center pin is made of a magnetized member. The first center pin is provided in a hole of the stator so that the first center pin is movable in the direction of the rotation axis. The galvano mirror unit further includes first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and an offset magnet provided to the stator. The offset magnet attracts the first center pin in a predetermined direction, thereby to prevent the deviation of the inclination of the first center pin in the hole.
With such an arrangement, since the offset magnet urges the first center pin in a predetermined direction, the deviation of the inclination of the first center pin is prevented. Thus, the rotation of the galvano mirror is stabilized.
According to still another aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, first positioning magnet provided to the rotor, and second positioning magnet provided to the stator. Each of the first and second positioning magnets including a portion of N-pole and a portion of S-pole. A neutral position of the rotor is obtained by the attraction of the first and second positioning magnets.
With such an arrangement, the galvano mirror is urged to its rotational neutral position without providing a separate spring member.
According to still another aspect of the present invention, there is a galvano mirror unit comprising, a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and positioning magnet provided to the stator. The first center pin includes a portion of N-pole and a portion of S-pole. The positioning magnet includes a portion of N-pole and a portion of S-pole. A neutral position of the rotor is obtained by the attraction of the first center pin and the positioning magnet.
With such an arrangement, the galvano mirror is urged to its rotational neutral position without providing a separate spring member.